1. Field of the Invention
The present general inventive concept relates to displaying information on data display instruments and, more particularly, to an apparatus and a method of displaying course information and a degree of deviation therefrom on electronic aircraft flight data display instruments even when the degree of course deviation exceeds the limits of the display instruments so that the instruments become saturated.
2. Description of the Related Art
A navigational system on an aircraft presents guidance cues to a pilot in terms of “steering commands.” These guidance cues are used to convey to the pilot whether the aircraft is on course or off course and are applied during multiple phases of flight. Specific examples of use include long-range en-route navigation and precision zero-visibility runway landings.
Guidance cues are generated when the aircraft is off course or “deviated” from a desired navigational course to an intended destination that has been programmed into the navigation system. Upon detecting a deviation, guidance cues are presented to the pilot in the form of steering commands such as “fly up” or “fly down” when vertical guidance is available, and/or “turn right” or “turn left” when lateral guidance is available.
Traditional implementations of these guidance cues have been presented via physical needles including a first needle that may move back and forth, or “deflect” to a left or a right of a center position, and a second needle that may deflect up or down of a center position. If both needles are in the center position, the aircraft is on the desired navigational course. If either needle is not in the center position, the needle is considered to be deflected and a steering command is generated to instruct the pilot as to the direction in which the aircraft should be maneuvered so that the deflected needle returns to the center position, thus returning the aircraft to the desired navigational course.
The degree of deflection of the first and/or second needle corresponds to the degree the aircraft has deviated from the desired navigational course. Small deviations are shown with small needle deflections while larger course deviations are likewise indicated via larger needle deflections. Thus, the amount that the pilot steers left/right or up/down, corresponds generally to the amount of needle deflection present to correct the navigational error.
The physical needle is limited by a range in that there is a maximum right deflection and a maximum left deflection. Since the degree of deflection relates to the degree in which the aircraft is off course, if the aircraft is significantly off course, the navigational error may be greater than what the physical needle can present, thus resulting in the needle being fully deflected or in a “pegged” position. When this condition occurs, the needle provides a misleading presentation.
For example, if a lateral position error is 5 nautical miles and the needle can only show a deviation of 3 nautical miles, the needle will be deviated to a maximum physical extent in either a left or right direction and in the pegged position. From the pilots point of view, there is no difference between a condition where the actual navigational error is 3 nautical miles and a conditional where the actual navigational error is greater than 3 nautical miles.
In this situation, the pilot will attempt to correct the heading by altering course in reliance of the pegged needle so that the needle returns to the center position. However, depending on the extent the aircraft is off course and the corresponding extent of pegging, the needle may remain in the pegged position for a period of time and possibly after significant course correction, which may cause the pilot to speculate as to the cause of why the needle is not moving. The pilot may assume that the needle is not moving because it is pegged, or the pilot may assume that the needle and/or another device is defective.
Even if the pilot speculates that the needle is pegged and is correct, the extent of pegging or heading deviation is unknown, which results in further speculation. Naturally, any pilot uncertainty is very dangerous even if the timeframe of uncertainty is merely a momentary window.